1. Field of the Invention
The present invention relates to an evaporated fuel treatment device of an engine.
2. Description of the Related Art
In an internal combustion engine designed to have the evaporated fuel produced in the fuel tank etc. adsorbed once by activated carbon in a canister and to have the evaporated fuel adsorbed by the activated carbon purged in the engine intake passage, it is necessary to purge the evaporated fuel adsorbed by the activated carbon into the intake passage as fast as possible so as to keep the adsorption capacity of the activated carbon from becoming saturated. During engine operation, however, there is the problem that when the purge action is stopped once and then restarted in a state where a large amount of evaporated fuel is adsorbed by the activated carbon, if the purge rate is increased for purging the evaporated fuel from the activated carbon to the inside of the intake passage as fast as possible, a large amount of evaporated fuel will be purged into the intake passage the instant that the purge action is restarted, so the air-fuel ratio will fluctuate by a large margin.
Therefore, there is known an internal combustion engine designed so that when a large amount of evaporated fuel has been adsorbed by the activated carbon just before the purge action is stopped, that is, when the purge vapor concentration just before the purge action is stopped is high, the purge rate at the time of the restart of the purge action is made small and when the purge vapor concentration just before the purge action is stopped is low, the purge rate at the time of restart of the purge action is made large (see Japanese Unexamined Patent Publication (Kokai) No. 5-223021).
The amount of the evaporated fuel adsorbed by the activated carbon just before the purge action is stopped and the amount of evaporated fuel adsorbed by the activated carbon when the purge action is restarted, however, are not necessarily the same. When the fuel tank becomes high in temperature and a large amount of evaporated fuel is produced, a large amount of evaporated fuel is adsorbed by the activated carbon in the time from when the purge action is stopped to when the purge action is restarted. Therefore, if the purge rate is increased at the time of the restart of the purge action just because the purge vapor concentration was low just before the purge actoin was stopped as in the above internal combustion engine, a large amount of evaporated fuel will be purged into the intake passage the instant the purge action is restarted and therefore the problem will arise of a large fluctuation of the air-fuel ratio.